We have noticed a number of genoni heat exchanger failures in apartment blocks that have had to drain the system for repairs. The fresh water causes corrosion and iron oxide sludge (manganite). For up to 1 million BTU, it is a 1 inch bypass system with a Dirtmag and a 20 inch 5 micron bag filter plus a flow meter. Up to 2 million BTU it is a 2 inch Dirtmag and a 40 inch 5 micron bag filter plus a flow meter. The flow rate for the 1 inch is 10 GPM and an UP15-42 is satisfactory. The 2 inch is at 45 GPM using an UPS26-150. The enclosed sketch shows an error by our tech, it is not 5 GPM for the 1 inch. It is in French as most of our plumbers are French speaking. The enclosed pictures show a sample of boiler water that was magnetised. The iron particles fell to the magnet. The yellow water was the same system after two months of bypass filtration. It is a relatively inexpensive insurance for the boilers.